Paper-based sensing (i.e. paper-based test devices) is an emerging technology that has advantages relative to traditional test strips in terms of cost and multiplexing. The concern of poor accuracy on paper-based sensors and paper test strips, due to the colorimetric measurement, has limited them from quantitative applications. In existing test strip applications, a user has to manually compare resultant colors to a set of colors on a separate reference card. This is neither user friendly nor reliable. Recently some companies have developed phone ‘apps’ to automate the test strip reading process using a phone camera.